BUYING YOUR FIRST TELESCOPE

PART I

"A GOOD PAIR OF BINOCULARS!"

Yes - the best first telescope is a good pair
of binoculars! The route to learning to appreciate what the skies have to offer
starts with gaining knowledge of the constellations and where things are to be
found; then getting a closer look with binoculars and what they can offer
(objects like Comet Hale-Bopp need these!); finally comes a telescope and what
more and different it has to offer. Each aspect of gaining knowledge of the
heavens has its own strengths and limitations. Learning them will allow you,
the observer. to use the proper tool for the observation you want to make.

So, when it comes to buying binoculars, what
do you need to know? To sum it up:

large
objective diameter

magnification
no greater than 7-8

proper
size exit pupil

good
eye relief

fully
multi-coated optics

BAK-4
Porro prisms

rugged
design

maybe
a couple of other goodies

Simple, right? Maybe not, so let's get into
some details.

First of all you need as large an objective diameter
as is feasible. Simply put, the larger the diameter, the more light can get
into your eye (and the fainter the objects you can view). However, there is a
fine interplay between the objective diameter, the magnification and the exit
pupil.

Second, when it comes to magnification,
usually 7-8X (power) is the most you can use and still hold your binoculars
steady. Third, the exit pupil is the diameter of the light beam as it exits the
eyepiece. You can calculate it by dividing the objective diameter by the
magnification. For the younger set, 6-7 millimeters is about the size of your
dark-adapted eye pupil. But, for older folks - beyond age 40 or so, this is too
much and an exit pupil of about 5 is more appropriate.

So, for a younger person, with a magnification
of 7X and an exit pupil of 7 mm., an objective diameter of 50 mm. is about
right (50 mm. divided by 7 [the magnification] is a little more than a 7mm exit
pupil. More than large enough).

But, for an older person, with a
magnification of 7X and an exit pupil of 5 mm., an objective diameter of 35 mm.
is about right.

In binocular jargon, the young person's
instrument would be a 7x50. That is, 7X magnification and 50 mm objective
diameter. While the older person's would be a 7x35 - or 7X magnification and 35
mm objective diameter.

Both the 7x50 and 7x35 are commonly available
binocular sizes; so you should not lack choices. The 7x50 binocular also has
the pseudonym of 'night glasses' because they were originally designed for that
purpose. However, the 7x35 is the 'night glass' for the older!

Fourth, consider eye relief, the distance
back from the eyepiece the image forms (at the exit pupil). If you wear glasses
and want to keep them on while viewing, you need good eye relief (i.e. 20 mm.
or more). This number is available from the manufacturer. But, it may be that
you will have to find this out for yourself - by looking through the binoculars
(with and without your glasses) to decide if it's suitable.

Fifth, the term, fully multi-coated, refers
to the optical coating that should be on every air-to-glass surface. Every time
light hits glass a small amount is reflected away. You don't want this. You
want the light to pass through with a minimum of trouble. When a surface is
coated, this reflection is minimized. With a multiple coatings system, it's
minimized even more. When light has the many, many air to glass passages to
make typical of binoculars, there are a lot of possibilities for light to be
reflected everywhere but straight through like you want (and need!). So you can
see why it's important for each surface to be coated. A quick way to judge this
is to look at the objective lens surface with a light source behind you. For
every white colored reflection you see, you have an uncoated surface.

Sixth, the prisms in your binoculars should
be made from BAK-4 glass, the best glass. This is a must for good light
transmission. They should also be the Porro prism
design to give the widest field through your instrument at the lowest cost.

Seventh, you should consider the mechanical
design of the binocular. There are three common types: Zeiss, American and
straight through. The latter are more difficult to make with wide, unvignetted fields of view. They are generally more
expensive and can probably be left off your list to consider, at least for
starters.

The very common (most common?) Zeiss types
are more vulnerable to dropping or mishandling than the American type. Most of
the Japanese and German made binoculars are Zeiss type (a notable exception is Fujinon binoculars). If you can get the American design
with the other parameters OK, you can expect a longer, trouble-free life of
use. (And, a good pair of binoculars should last YOU a lifetime!).

Finally, some other things you might like are
a tripod mount or rubber coated barrels. Both can make life easier. Also look
at the guarantee. Does the manufacturer with a 30 day guarantee have the same
faith in their product as one that has a life time guarantee?

All these things are not going to be found in
$25 binoculars; but you don't need $1000 for a good pair either. Start your
buying adventure by looking in catalogs and stores and seeing what's available.
Look for what we've just discussed. Maybe you can look through various models
at star parties and ask the owners how their particular model performs. If you
can find a store with more than one model, look through all that are in your
price range. Things you might consider are: How heavy are they? Will you be
comfortable holding them after a few minutes? Is the image in focus from edge
to edge or is it sharp in the center and blurry around the edges. Does the
image have good contrast. And can I really tell the difference between the $250
model and the $500 pair.

The difference between cheap models and more
expensive ones are obvious. But as the price gets higher the differences become
less. Only you know if you can justify that $500 pair when the image through
the $250 pair was almost as good. Price alone is not always an indication of a
good image. If the image through a $500 pair isn't as good as the $250 pair,
why spend the extra money?

Armed with some basic information you can be
an informed buyer and avoid the pitfalls that you shouldn't have to fall into.

Naming Your Star

As many of you know, there are companies that
advertise that folks can have a star named for themselves, friends, etc.
Recently, there was a lot of publicity about the naming of a Delaware State
Star - now called the "Delaware Diamond".

The companies indicate that your named star
will be included in some sort of publication and registered with the US
Copyright Office - adding an air of authenticity of the naming process. However
there is NOTHING OFFICIAL about the naming, it is not sanctioned by the IAU which has the worldwide authority in the official
star naming procedure.

Mount
Cuba Astronomical Observatory gets
calls asking for information on whom to contact to get a star named. In the
past, we have given that information over the phone - with some words of
reminder that the names are NOT official. I have been uncomfortable with this,
so we will not be doing it in the future.

I contacted Brian Marsden at SAO and, through him, Johannes Andersen, who is the General Secretary of
the IAU. The IAU WebPages on the subject
can be found by clicking here.